Fix merge attributes tool sets skipped attributes to null (fix #13231)

Author: nyalldawson

src/app/qgisapp.cpp

@@ -6150,11 +6150,15 @@ void QgisApp::mergeAttributesOfSelectedFeatures()
   vl->beginEditCommand( tr( "Merged feature attributes" ) );
 
   QgsAttributes merged = d.mergedAttributes();
+  QSet<int> toSkip = d.skippedAttributeIndexes();
 
   Q_FOREACH ( QgsFeatureId fid, vl->selectedFeaturesIds() )
   {
     for ( int i = 0; i < merged.count(); ++i )
     {
+      if ( toSkip.contains( i ) )
+        continue;
+
       vl->changeAttributeValue( fid, i, merged.at( i ) );
     }
   }

src/app/qgsmergeattributesdialog.cpp

@@ -586,8 +586,6 @@ QgsAttributes QgsMergeAttributesDialog::mergedAttributes() const
     return QgsAttributes();
   }
 
-  QgsFields fields = mVectorLayer->fields();
-
   QgsAttributes results( mTableWidget->columnCount() );
   for ( int i = 0; i < mTableWidget->columnCount(); i++ )
   {
@@ -604,7 +602,7 @@ QgsAttributes QgsMergeAttributesDialog::mergedAttributes() const
     if ( idx >= results.count() )
       results.resize( idx + 1 ); // make sure the results vector is long enough (maybe not necessary)
 
-    if ( comboBox->itemData( comboBox->currentIndex() ) != "skip" )
+    if ( comboBox->itemData( comboBox->currentIndex() ).toString() != "skip" )
     {
       results[idx] = currentItem->data( Qt::DisplayRole );
     }
@@ -616,3 +614,25 @@ QgsAttributes QgsMergeAttributesDialog::mergedAttributes() const
 
   return results;
 }
+
+QSet<int> QgsMergeAttributesDialog::skippedAttributeIndexes() const
+{
+  QSet<int> skipped;
+  for ( int i = 0; i < mTableWidget->columnCount(); ++i )
+  {
+    QComboBox *comboBox = qobject_cast<QComboBox *>( mTableWidget->cellWidget( 0, i ) );
+    if ( !comboBox )
+    {
+      //something went wrong, better skip this attribute
+      skipped << i;
+      continue;
+    }
+
+    if ( comboBox->itemData( comboBox->currentIndex() ).toString() == "skip" )
+    {
+      skipped << i;
+    }
+  }
+
+  return skipped;
+}

src/app/qgsmergeattributesdialog.h

@@ -37,6 +37,11 @@ class APP_EXPORT QgsMergeAttributesDialog: public QDialog, private Ui::QgsMergeA
     ~QgsMergeAttributesDialog();
     QgsAttributes mergedAttributes() const;
 
+    /** Returns a list of attribute indexes which should be skipped when merging (eg, attributes
+     * which have been set to "skip"
+     */
+    QSet<int> skippedAttributeIndexes() const;
+
   private slots:
     void comboValueChanged( const QString & text );
     void selectedRowChanged();